1. Field of the Invention
The invention relates to an electric pump. More particularly, the invention relates to an electric pump that is reduced in size in the axial direction by arranging an electric motor on the radially outer side of a pump and integrating a permanent magnet of the electric motor with an outer gear of the pump.
2. Description of the Related Art
In a vehicle in which an engine automatic stop control for stopping or starting an engine based on the operating state of the vehicle is executed, it is necessary to ensure required hydraulic pressure for a hydraulic circuit of a transmission at the time of engine start. Therefore, the vehicle in which the engine automatic stop control is executed includes an electric pump that supplies hydraulic pressure to the hydraulic circuit of the transmission at the time of engine start, in addition to a mechanical pump that supplies hydraulic pressure using the rotation of the engine (see Japanese Patent Application Publication No. 2001-99282 (JP-A-2001-99282)). A vehicle that employs an anti-lock brake system (hereinafter, referred to as “ABS”) includes an electric pump for the ABS control in order to ensure required hydraulic pressure for activating the ABS. Preferably, these electric pumps should be as small as possible in view of the mounting space.
Japanese Patent Application Publication No. 2003-129966 (JP-A-2003-129966) describes an electric pump that is reduced in size in the axial direction by arranging an electric motor on the radially outer side of a pump and integrating a permanent magnet of the electric motor with an outer gear of the pump. FIG. 5 shows an axial sectional view of an existing electric pump 110 having a similar structure to that of the electric pump described in JP-A-2003-129966. The electric pump 110 is formed by arranging a stator portion 122 and a permanent magnet 124 that constitute a motor 120 on the radially outer side of an outer gear 132 and inner gear 134 that constitute a pump 130 and connecting the permanent magnet 124 of the motor 120 with the outer gear 132 of the pump 130. Then, the motor 120 and the pump 130 are arranged between a housing 140 and a housing 142, and the housing 140 and the housing 142 are connected to each other when a bolt 144 is passed through a flange 141 and a flange 143 that are formed at ends of the housing 140 and the housing 142, respectively. Then, when the stator portion 122 is energized, the permanent magnet 124 of the motor 120 and the outer gear 132 of the pump 130 rotate together with each other, and the inner gear 134 of the pump 130 is rotated in accordance with the rotation of outer gear 132. As a result, pumping action is produced. However, in the motor oil pump shown in FIG. 5, the flanges need to be formed at the housings in order to connect the housings to each other. This leads to an increase in size of the electric pump in the radial direction. In addition, the bolt for connecting the flanges to each other is required. This leads to an increase in the number of components.